1. Field of the Invention
The present invention generally relates to a passenger restraint system that controls the operation of a passenger restraint device in accordance with the state of roll angular velocity centered about a longitudinal axis of a vehicle.
2. Background Information
A passenger restraint system is disclosed in Japanese Laid-Open Patent Publication No. 9-240399, in which a roll angular velocity sensor is used to detect the roll angular velocity of a vehicle about its longitudinal axis. The passenger restraint system of this publication has a control unit that actuates a passenger restraint device when the vehicle""s rolling rate and rolling angle reach or exceed prescribed values. In particular, a first determination is made by the control unit to determine whether the vehicle""s rolling rate reaches or exceeds a prescribed value for the rolling rate. Then, after a period of time, a second determination is made by the control unit to determine whether the vehicle""s rolling angle reaches or exceeds a prescribed value for the rolling angle.
There are situations in which the passenger performs an operation that causes the vehicle to recover after the vehicle""s rolling rate reaches or exceeds the prescribed value. In order to handle such situations, when the second determination does not occur within a prescribed amount of time after the first determination becomes affirmative, the aforementioned known system subtracts a prescribed angle from the roll angle successively and resets the first and second determinations when the roll angle obtained after subtracting falls below a minimum value.
In view of the above, there exists a need for an improved passenger restraint system. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
It has been discovered that in the aforementioned passenger restraint system, if a vehicle falls down an embankment, then it is possible for the system not to accurately calculate the roll angle. In particular, in this situation, the roll angular velocity first exceeds the prescribed value and the first determination becomes affirmative when the vehicle shifts from a state of normal travel to a state of falling down the embankment. Afterwards, the roll angle does not change very much while the vehicle is traveling down the embankment without rolling over. Consequently, the prescribed amount of time elapses before the roll angle exceeds the prescribed value (second determination) and this system successively subtracts the prescribed angle from the roll angle. Thus, in such a case where the vehicle travels down an embankment without initially rolling over but rolls over a short while afterwards, there is the possibility that a difference will exist between the actual roll angle and the calculated roll angle. Thus, the system may not accurately calculate the roll angle.
Therefore, an object of the present invention is to eliminate the occurrence of a difference between the actual roll angle and the calculated roll angle by not executing subtraction from the roll angle in cases where the passenger does not perform a vehicle recovery operation after the roll angular velocity exceeds the prescribed angular velocity and, thus, to actuate the passenger restraint device more appropriately in situations where the vehicle rolls over thereafter.
In accordance with the present invention, a passenger restraint system is provided that basically comprises a roll angular velocity detecting device, a roll angle calculating device, a steering angle detecting device, a passenger restraint device and a control unit. The roll angular velocity detecting device is configured to detect a roll angular velocity about a longitudinal axis of a vehicle. The roll angle calculating device is configured to calculate a roll angle of the vehicle based on the roll angular velocity detected by the roll angular velocity detecting device. The steering angle detecting device is configured to detect a steering angle. The passenger restraint device is configured to restrain a passenger. The control unit is configured to actuate the passenger restraint device when the roll angular velocity detected by the roll angular velocity detecting device exceeds a prescribed angular velocity and the roll angle calculated by the roll angle calculating device exceeds a first prescribed angle. The control unit is further configured to subtract a prescribed value from the detected roll angle successively, when the roll angular velocity detected by the roll angular velocity detecting device exceeds the prescribed angular velocity and the steering angle detecting device detects a steering angle oriented toward a side of the vehicle in which the vehicle is rolling before calculation of the roll angle by the roll angle calculating device exceeds the first prescribed angle. The control unit is further configured to reset a determination of whether or not the roll angular velocity is greater than or equal to the prescribed angular velocity and a determination of whether or not the roll angle is greater than or equal to the first prescribed angle, when the roll angle obtained after subtracting falls below a second prescribed angle.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.